1. Field of the Invention
The present invention relates to a projection display apparatus, and more particularly to a projection display apparatus having a curved projection screen.
2. Description of the Related Art
A projection display apparatus is a system that produces images in image display devices such as specially manufactured tiny cathode ray tubes (CRTs), liquid crystal devices, or the like. The projection display apparatus enlarges and projects the images on a large screen using projection lenses, the demands of which increase day by day in response to larger screens obtained to satisfy consumers' demands.
Such a projection display apparatus is classified into a front projection type and a rear projection type depending upon projection fashions. The front projection type projects images in the same direction as the images are viewed, and the rear projection type projects images in the opposite direction to a user who views the images, that is, from the rear of the screen. The rear projection type is widely used in a form of projection TV's that can provide clear views even in bright surroundings.
FIG. 1 is a view for schematically showing a structure of a conventional flat projection television set. Such a projection television set is structured to focus image sources on a flat-type large screen 300 through projection lenses 200 each having a predetermined magnification, and the image sources are formed on the fluorescent screens of red (R), green (G), and blue (B) monochromatic CRTs 100.
In the above projection display apparatus, the optical characteristics of the screen play an important role, being dominant over image quality, and are very important in the large projection television, in particular, demanding a high image quality as in a high definition (HD) television.
FIG. 2 is a view for showing in detail a portion of the large screen 300 in a conventional projection television set of FIG. 1. In FIG. 2, the conventional screen 300 for a projector is formed with a Fresnel screen 310 and a Lenticular screen 320. With the Fresnel screen 310 and the Lenticular screen 320, the amount of light can be controlled as well as a view distance can be controlled depending upon an ambient focal length.
In order to receive respective light rays from image sources, refract the respective light rays, and display images with a nearly uniform luminance over a wide view angle, the screen 300 has a Fresnel lens 310 converting light rays magnified and incident from the projection lenses 200 into parallel light rays. In front of the surface of the Fresnel lens 310, that is, in front of the light emission surface, a Lenticular lens 320 formed with plural protrusion-type unit lenses 321 in parallel connection is disposed adjacent to the Fresnel lens 310 as a light scattering unit for scattering the parallel light rays that come out of the Fresnel lens 310 so as to form images.
Protrusions 323 are formed on the parallel junction portions of the respective protrusion-type unit lens 321 of the light emission surface of the Lenticular lens 320, and black stripes 323a are formed that are painted in black on the front sides of the protrusions 323. The protrusions 323 and the black stripes 323a absorb light from an external light source such as fluorescent lamp light, sun light, and the like, so that the contrast of images formed on the front surface of the Lenticular lens 320 can be enhanced.
A general projection television set projects light on the screen from three monochromatic CRT tubes to produce desired images. The properties of the view angle and the ambient luminance are important in such a projection television, as compared to a direct view television.
As high definition (HD) format screens have become larger and wider, in-room small theaters such as home theaters are actively being formed. Such a large and wide screen requires different concepts from the light amount controls of the existing projection television set. More specifically, since a user watches the entire wide screen in an area such as a living room and in a central location of the television set, it is preferable to have a bright screen from its central portion out to its edge portions for the user's watching.
In a light amount control structure of an existing projection television set, the concentration angle for circumferential edges is set to a remote distance rather than a short distance. This means that an existing projection television set is designed to enable plural viewers to watch programs at a large area rather than as a component of a home theater and to have a structure considering all viewing situations at plural areas of the edges of the set. The Fresnel lens has a limitation of short focal length for large and wide screens, which is because the height and slope of the Fresnel zone increase toward the edges of the Fresnel screen (from its center). Thus, it is difficult to form a short focal length at circumferential edges for a large wide screen due to the limitation of its production process.